This invention relates generally to a circuit and a method for coupling a variable width pulse through a pulse transformer to allow all of the information in the incoming signal to be successfully transmitted across transformer couplings for use in driving other equipment. The invention is especially useful for powering a brushless motor commutation circuit.
The need has long existed for a better, less expensive way in which to drive a switching, or driver circuit without having the relatively lower current or voltage of the control circuit become affected by the relatively larger current or higher voltage in the driver circuit (i.e. isolation). One solution to this problem has been to use opto-isolators. This scheme generally involves the illumination of a light source by the control circuit, and the reception of light radiation from the light source by an optical relay in the driver circuit. In this manner, since the only connection between the two circuits consists of a radiative light, the current and voltage levels of the two circuits could be grossly dissimilar without the possibility of the voltage and current of one becoming affected by the voltage or current of the other.
The main problem with the opto-isolator scheme, is its susceptibility to extraneous electromagnetic interference. Electromagnetic interference can arise via unwanted conduction, induction, or radiation from unexpected sources outside the circuit. The need for circuitry designs specifically resistive to electromagnetic interference has been so great as to have created a specialty within the electronic arts. However, a light sensor suitable for the aforementioned optical coupling must, of necessity, be sensitive to and, therefore, easily interferable by electromagnetic interference. In space satellite applications where the radiation levels are high the interference is more severe. In addition, the cost of optoisolators tends to add significantly to the cost of circuit design.